Proximity sensorKoustubh ChakrabortyB.Tech 3rd year (ECE)Roll No- 18700312067

Contents:

1. Definition

2. Types of Proximity Sensors

3. Inductive Proximity Sensors

4. Capacitive Proximity Sensors

5. Ultrasonic Proximity Sensors

6. Optical Proximity Sensors

7. Conclusion

8. Reference

Definition

Detection occurs when object approaches within detection range

All sensors performing non contact sensing are included in proximity sensors

Proximity Sensors

Inductive

Capacitive

Ultrasonic

Optical

Reflective

Direct

Retro Reflective

Polarized Reflection with

reflectorThru Beam

Types of Proximity Sensors

Inductive Proximity Sensors Detects Metallic objects without physical contact

A coil and high frequency oscillator is used

Operating distance depends on

Coil’s size

Target’s shape, size, material

Components & Working Principle Main components & their work

Coil• Generates high frequency magnetic field in front

of face

• Metallic target absorbs some magnetic energy

Oscillator• Oscillation circuit is affected by the absorption of

energy

Detector• Change in oscillation is detected with threshold

circuit

Continued…

Components & Working Principle

Components & Working Principle

Output Circuit• Output of circuit changes due to change in oscillation

Advantages

• Accurate• High switching rate• Works in harsh environmental condition

Disadvantages

• Detects only metallic target

Applications

• Metal detectors• Car washes

ADVANTAGES AND APPLICATIONS

Capacitive Proximity Sensors Detects metallic objects as well as non-

metallic objects(liquid, plastic, wooden material etc)

Uses variation of capacitance between sensor and object

Distance down to 1 micro inch can be measured

All targets having dielectric constant more than air can be detected

Components & Working Principle Main Components

Plate

Oscillator

Threshold Detector

Output Circuit

Continued…

CAPACITIVE PROXIMITY SENSOR

Working Principle

Plate acts as one plate of capacitor

Other plate being the target

Air is dielectric medium

Change in capacitance initiates oscillation

This is identified by threshold circuit which switches the output

Advantages

• Metallic & non-metallic targets• High speed• Good stability• Low cost and power consumption

Disadvantages

• Affected by temperature and humidity• Less accurate• Difficult to design

Applications

• Mobile Phones • Laptop track pads and more

ADVANTAGES AND APPLICATIONS

Ultrasonic Proximity Sensors

Uses ultrasonic sound wave for detection

Used frequency is higher than audible range

Can measure distances very accurately

Provides good sensing for large objects with hard surface

Ultrasonic Sensors Working Principle

Quartz-crystal transducer generates ultrasonic sound wave

Emitter transmits the sound wave

Waves strike objects within the field of detection

Movement disrupts the sound wave

Reflected back to the system’s receiver.

ULTRASONIC PROXIMITY SENSORS

Advantages

• Not affected by atmospheric dust, snow, rain etc.• Sensing distance more than capacitive and inductive

Sensors• Works in adverse condition

Disadvantages

• Difficult to sense from soft, curved, thin or small objects

Applications

• Ultrasonic thru beam sensors in bottle counting machine

• Vehicle detection in barrier system

ADVANTAGES AND APPLICATIONS

Optical Proximity Sensors

Senses any object within 10 meters range

Uses an LED in either infrared or visible light spectrum to transmit

Photodiode detects the light generated

Generally light sources pulse the infra-red light on and off at a fixed frequency.

Sensor detects object when it disrupts light beam

Two types- Reflective type And Thru beam type

Thru Beam type

Emitter and receiver housed separately

Object is detected when light beam is disrupted

Allows the longest range

THRU BEAM TYPE

Reflective type

Emitter and receiver are housed together

Object is detected by means of reflection

Three types

1. Direct reflection

2. Reflection with reflector

3. Polarized reflection with reflector

1. Direct reflection

Light reflected off the object is detected

Surface and colour determines the sensing distance

2. Reflection with reflector (Retro Reflective)

A reflector is needed

Disruption of the light beam between Sensor and reflector is detected

Rays emitted are almost totally reflected towards the receiver so longer sensing distance is allowed

DIRECT REFLECTION

REFLECTION WITH REFLECTOR

3. Polarized Reflector

Contain polarizing filters in front of the emitter and receiver

Filters are 90° out of phase with each other

Polarized light if reflected off an object, remains polarized

Polarized light if reflected off a depolarizing reflector, it is depolarized

Receiver can only detect reflected light that has been depolarized

POLARIZED REFLECTION WITH REFLECTOR

Advantages

• Effective in dusty environments• Focused beam• Higher sensing distance• Immune from interference

Disadvantages

• Expensive

Applications

• Lift door mechanisms• Components positioning sensing• Security & safety • Counting objects in conveyer belts

ADVANTAGES AND APPLICATIONS

Conclusion

Machine tools, woodworking machines, packaging machines and other types of machinery.

Further applications are automatic door units such as garage doors or doors inside buildings, elevator doors or doors inside railway coaches.

The building and automotive sector are further industries using high volumes of proximity sensors.

REFRENCES http://literature.rockwellautomation.com/idc/groups/

literature/documents/ca/c116-ca502_-en-p.pdf http://en.wikipedia.org/wiki/Proximity_sensor http://www.fargocontrols.com/sensors.html http://www.autonics.co.in/products/products_2.php?

big=01&mid=01/01 http://www.ia.omron.com/support/guide/41/

overview.html http://www.sensorcentral.com/photoelectric/

proximity01.php http://www.engineershandbook.com/Components/

proximitysensors.htm http://www.ab.com/en/epub/catalogs/

12772/6543185/12041221/12041223/Retroreflective-and-Polarized-Retroreflective.html

Thank You!